Electronic printing includes all ink jet printing, such as continuous ink jet printing, and all other systems wherein images are dried to fix the image on the substrate, as well as ionography, electrophotography, and all other systems wherein toner is fused to fix the image on the substrate. Current large scale electronic printing presses, typified by the Scitex 3500/3600 family, manufactured by Scitex Digital Printing, Inc., of Dayton, Ohio, are configured with a standard fuser/fixer or fixer/dryer system and are capable of drying at high speed, and full width.
The design of a typical fixer/dryer is very much related to the designs of fixers in general use in the printing industry. Typically, dryers are purchased as standard configurations, which are available with few options. They can be used at lower power if they are to be used at low speed, but standard products are generally not modular in the sense to be described below.
Conventional printing presses arrange all the apparatus for printing in a tower. Paper is fed to the tower by appropriate paper feeding apparatus using either sheets of paper, or a continuous web of paper. Typical color printing presses utilize multiple "towers". The paper is fed sequentially from one tower to the next, each tower printing a particular color (or sometimes a transparent coating). For printing processes which require fixing of one color ink before the next color ink is printed, a standard fixer/dryer is used between towers.
When it is desired to print on both sides of a substrate, there are several options in common usage. In one common web press configuration the first side is printed in a first tower and then a second tower is used for printing on the reverse side. In this type configuration, a turnbar is required between towers. A turnbar is an arrangement of rollers which have the effect of inverting the web so that the unprinted side of the paper is available for printing in a subsequent tower. Typically, at least four colors are needed on each side of the paper, so either four towers (in offset presses that can print on both sides of the paper at each tower) or eight towers (such as in cases where the print heads cannot operate upside down) are required. Obviously, the result is a long printing press, especially if dryers are required between print impressions. Long printing presses have associated problems which include excessive floor space requirements and, for digital printing systems, excessive data memory requirements.
Furthermore, in a multi-color printing process, such as a 4-color process, it is necessary to print black, cyan, magenta and yellow on paper with an accuracy of 1 pixel (1/240th of an inch), or better, anywhere on a 17".times.34", or larger, image. Although conventional printing processes have minimal added moisture due to printing, certain ink jet processes introduce noticeable moisture content, particularly when using multiple colors for printing. Furthermore, dimensional characteristics of the paper adversely affect image quality. Paper expands and contracts due to its moisture content in a non-isotropic manner with lots of hysteresis. Although drying can be used to remove moisture, if dryers are used between each color printed, large dimensional changes to the paper, or substrate "stretch" or "shrink", can occur, again adversely affecting image quality. Since paper responds nearly instantaneously to the addition or removal of water, "good" printing of multiple colors has to be done in just a few seconds.
It is seen, then that there is a need for an improved electronic printing architecture which overcomes the problems associated with prior art electronic printing system architectures, and, in particular, can be applied to a digital color press printing system.